M. Heydari-Malayeri - Paris Observatory

A stage in the evolution of an → asymptotic giant branch star,
when all the helium
in the core is fused into carbon and oxygen. No more fusion takes place in the core, and
as a result the core contracts. The core contraction generates a sufficient
temperature for fusing the surrounding layers of helium.
Since helium shell burning is unstable, it causes
→ helium shell flashes.